Spectral Reflectance

Different surface features reflect or absorb the sun's electromagnetic radiation in different ways. The reflectance properties of an object depend on the material and its physical and chemical state, the surface roughness as well as the geometric circumstances (e.g. incidence angle of the sunlight). The reflectance of a material also varies with the wavelength of the electromagnetic energy. These differences in reflectance make it possible to identify different earth surface features or materials by analyzing their spectral reflectance signatures. These signatures are visualized in spectral reflectance curves that show the percent reflectance as a function of wavelengths.

Vegetation

In general, healthy vegetation is a very good absorber of electromagnetic energy in the visible region. Chlorophyll strongly absorbs light at wavelengths around 0.45 (blue) and 0.67 µm (red) and reflects strongly in green light, therefore our eyes perceive healthy vegetation as green. Healthy plants have a high reflectance in the near-infrared between 0.7 and 1.3 µm. This is primarily due to the internal structure of plant leaves. As this internal structure varies amongst different plant species, the near infrared wavelengths can be used to discriminate between different plant species.

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